Hereditary hemochromatosis affects six per thousand Caucasians. Dr. Kushner and his collaborators are defining the proportion of affected homozygotes that develop disease-related morbidity in order to justify large-scale population screening programs. The clinical manifestations of hereditary hemochromatosis may range from simple laboratory abnormalities with no organ dysfunction to a ""full-blown"" clinical syndrome, including cirrhosis of the liver, heart failure, diabetes, endocrine failure, and arthritis. The molecular basis for the enormous variation in disease severity is not known.